This invention relates to a method of making a dishwashing composition and the dishwashing composition so produced. The composition is primarily intended for use with both residential and commercial automatic dishwashers. The agglomerated granules produced in accordance with the method of the present invention form a very stable product having excellent flow characteristics and a high degree of uniformity among the particles forming the composition.
The dishwashing composition of the present invention accomplishes its primary purpose of thoroughly cleaning dishes, pots, pans, silverware and the like while exhibiting excellent corrosion inhibition and fine china overglaze protection. Excellent results are consistently obtained due to the uniformity of the distribution of components among the agglomerated particles formed by the method of the present invention. A feature of the present invention is the use of an aqueous solution of sodium hypochlorite which provides a uniform amount of available chlorine to the dishwashing granules.
Prior art attempts to combine excellent cleaning properties with overglaze protection and corrosion inhibition properties in automatic dishwashing compositions have had varying degrees of success. The method and composition of the present invention are neither disclosed nor suggested by any of the following patents which are believed to represent the closest prior art.
U.S. Pat. No. 3,491,028 of Crotty et al. discloses a dishwashing composition comprising an alkaline material which may be an alkaline builder, or a combination of an alkaline builder and a caustic material, and a chlorinating agent which may be lithium hypochlorite, or lithium hyphochlorite in combination with sodium or potassium dichlorocyanurate. Some of the preferred embodiments include sodium orthosilicate or sodium metasilicate. It is stated at column 3, lines 32-34, that it is essential in formulating the composition that all ingredients be kept as dry as possible prior to mixing. This patent teaches away from the present invention wherein the chlorinating agent is formed from an aqueous solution of sodium hypochlorite.
U.S. Pat. No. 3,817,869 of Ries et al. discloses a substantially sequestrant-free dishwashing composition comprising an ionizable salt, an alkali metal silicate, a chlorine-yielding bleach and a nonionic synthetic detergent. The preferred method of forming the compositions disclosed in the patent is to simply admix all of the components to produce the final product, although other methods are merely named, including pan agglomerating, slurry or moistening of the components followed by a drying procedure. This patent teaches away from the use of sequestrant builder salts as used in the present invention and does not disclose or suggest the method of making the composition according to the present invention which results in a uniform product having excellent chlorine stability.
U.S. Pat. No. 3,825,498 of Altenschopfer et al. discloses a dishwashing composition which is either free of phosphates or has a greatly reduced phosphate content. The composition comprises about 90%-5% of a water soluble alkali silicate and about 5%-90% of a polyhydroxy carboxylic acid containing polymers built predominantly from chemical units unrelated to the present invention. The method used to form the patented composition is quite dissimilar from the method of the present invention.
U.S. Pat. No. 3,826,748 of Finck discloses a non-phosphate dishwashing composition containing a water soluble aminopolycarboxylic compound, sucrose and an overglaze protector such as aluminum acetate, aluminum formate, alkali metal aluminum orthophosphates, alkali aluminate, zincate and berylliate, boric acid, boric anhydride, and mixtures thereof. The compositions may contain a bleaching agent capable of liberating hypochlorite chlorine and/or hypobromite bromine on contact with aqueous media, as well as nonionic surface active agents. Brominated and chlorinated trisodium phosphate, a dry product formed by the reaction of the corresponding sodium hypohalite solution with trisodium phosphate (and water as necessary), is listed among a large number of other hypohalite-liberating agents. It is stated at column 5, lines 43-46 that the compositions according to the patent are usually prepared by dry blending the ingredients to form a dry particulate product such as a free flowing granular composition or powder. This statement teaches away from the use of an aqueous solution of sodium hypochlorite as a separate ingredient in the preparation of the patented compositions. In addition, the patent teaches away from the present invention by excluding phosphates from the composition.
U.S. Pat. No. 3,852,209 of Hofmann has a disclosure which is substantially identical to U.S. Pat. No. 3,826,748. This patent is also concerned with a phosphate-free dishwashing composition prepared by dry blending the ingredients (column 5, lines 60-63). Accordingly, this patent may be distinguished from the present invention for the same reasons as U.S. Pat. No. 3,826,748.
U.S. Pat. No. 3,966,627 of Gray discloses a dishwashing composition directed to the problem of overglaze attack. The composition comprises a major proportion of a water soluble builder salt, an aluminum silicate and may include various types of detergents and hypohalite-liberating agents, such as those disclosed in U.S. Pat. Nos. 3,826,748 and 3,852,209. It is stated at column 8, lines 22-26 that there is nothing critical in the selection of the bleaching agent. Furthermore, this patent does not disclose what methods are used to form the patented compositions and, accordingly, neither anticipates nor renders the present invention obvious.
In contrast, the present invention results from the discovery that an aqueous solution of sodium hypochlorite can be used to produce a stable, uniform and effective dishwashing composition.